Vehicle with a steerable wheelset

ABSTRACT

A vehicle where respective inwardly inclined wheels ( 15 ) of a steerable wheelset run on respective inwardly sloping faces ( 54 ) of a guideway having centreline ( 39 ). The vehicle having sensing means for sensing lateral didsplacement of the wheelset relative to a longitudinal reference path. The sensing means signalling a control system including actuating means to steer the wheelset in response to sensed lateral displacement thereof.

TECHNICAL FIELD

This invention relates to a vehicle with a steerable wheelset. Whilstthe invention is primarily described with an embodiment particularlysuited for use with Automated Guideway Transit (AGT) systems of the typewhich use small, individual vehicles, capable of operating at highspeeds, the present invention is also suitable for use with a variety ofother rail or guideway systems.

BACKGROUND

There are a number of known vehicles adapted to travel on rail orguideway systems which have steerable wheelsets.

One such system is disclosed in U.S. Pat. No. 4,982,671 (Chollet et al),and relates to a track guided vehicle. Such a vehicle is supported onbogies, where each bogie contains two wheelsets. Magnetic (or other)sensors are used to detect the lateral position of the bogie withrespect to the track on which it is running. At least one sensor detectsthe angle between the two wheelsets. The two wheelsets are connected vialinkages and actuators, such that the angle between the wheelsets can bealtered to steer the bogie. A servo-control circuit receives signalsfrom the sensors and controls the actuators to steer the wheelsets inresponse to the detected lateral position of the bogie.

Another known system is disclosed in European Patent 374,290 (Girod etal), and relates to a track guided vehicle. Such a vehicle comprisesfour wheels that can be independently steered. Laser sensors, located atthe front and rear of the vehicle, are used to detect the differencebetween the track centreline and the vehicle longitudinal axis. Aservo-control mechanism controls the steering actuators in order tosteer the wheels in response to the sensed signals.

A disadvantage of both of these arrangements is that the lateral forcesat the wheel-rail contact zone must serve a dual function, namely tosteer the bogie and to oppose any lateral force, such as the centrifugalforce experienced by a vehicle while cornering. Consequently the forceavailable for steering the bogie is limited to the difference betweenthe total available force and that already being used to oppose anyexternal lateral forces. In a rail application where a steel wheel rollson a steel rail, the total available force may be very low. Thisavailable force may be substantially required to react centrifugalforce, with very little remaining force available to steer the wheelsetleading to frequent contact between the wheel flanges and the rails.

A further known system is disclosed in U.S. Pat. No. 5,730,064 (Bishop),and relates to a self-steering bogie for track guided vehicle. Thewheelsets are arranged such that a curvature in the rail generates atwist angle between the two wheelsets in the bogie when viewed in endelevation. The mechanism connecting the two wheelsets is arranged so asto steer the wheelsets, in response to rail curvature. A disadvantage ofthis arrangement when applied to small vehicle guideway systems, whichtypically use much sharper curves than normal rail systems, is the steererror resulting from twist angle supplied by rapidly changingsuperelevation. This may add to or subtract from the ideal steeringangle required, causing the wheelset to deviate from its idealised path.

Preferably the present invention overcomes the above mentioneddisadvantages by providing a vehicle with a steerable wheelset in whichthe effect of lateral or disturbing forces on the vehicle is minimised.

SUMMARY OF INVENTION

In one aspect the present invention is a vehicle with at least onesteerable wheelset adapted to run on a guideway having two primaryrunning faces laterally offset about a guideway centreline, the wheelsetcomprising a pair of wheels, each wheel located on opposite sides of thewheelset adapted to engage with a respective one of the two primaryrunning faces, the vehicle further comprising sensing means for sensinglateral displacement of the wheelset with respect to a longitudinallydisposed reference path, the sensing means producing a signal for acontrol system operably connected to an actuating means to steer thewheels in response to the sensed lateral displacement, characterised inthat the axes of rotation of the wheels and the primary running facesare inclined downwardly towards the guideway centreline.

In a first embodiment each wheel exerts an engagement force with itsrespective primary running face, the engagement force on each wheelcomprising a perpendicular component to its respective primary runningface and a parallel component to its respective primary running facesubstantially transverse to the guideway centreline, wherein horizontalforces acting on the wheelset substantially perpendicular to theguideway centreline are substantially resisted by the sum of of thehorizontal vectors of the perpendicular components.

In a second embodiment embodiment each wheel exerts an engagement forcewith its respective primary running face at a contact zone, theengagement force on each wheel comprising a first componentperpendicular to its respective primary running face and a secondcomponent parallel to its respective primary running face substantiallytransverse to the guideway centreline, wherein a first planeperpendicular to the axis of rotation of one of the wheels passesthrough its respective contact zone, and a second plane perpendicular tothe axis of rotation of the other wheel passes through its respectivecontact zone, the first and second planes intersecting along anintersection line disposed above and between the wheels, whereinhorizontal forces acting on the wheelset substantially transverse to theguideway centreline at or near the intersection line are substantiallyresisted by perpendicular components of the engagement forces acting atthe primary running faces, such that substantially all of the parallelcomponents of the engagement forces acting at the primary running facesare available to steer the wheelset.

Preferably the intersection line passes through the centre of gravity ofvehicle.

It is preferred that the sensing means comprises at least one sensorlocated either ahead or behind the wheelset, or laterally offset withthe wheelset. Alternatively the sensing means comprises at least twosensors, one of which is located ahead of the wheelset and the other islocated behind the wheelset.

It is preferred that the longitudinally disposed reference path issubstantially contiguous with the guideway centreline.

Alternatively, it is preferred that the longitudinally disposedreference path is substantially parallel to, but laterally offset fromthe guideway centreline.

It is preferred that a secondary running face lies immediately adjacentto, and substantially parallel to, at least one primary running face.

It is preferred that the longitudinally disposed reference path iscontiguous with the second running face,

Alternatively, it is preferred that a secondary running face liesimmediately adjacent to and substantially parallel to each primaryrunning face and the longitudinally disposed reference path iscontiguous with the lateral centreline between the respective twosecondary running faces.

It is preferred that at least one of the wheels also incorporates aflange, adapted to engage with the secondary running face.

It is preferred that the control system calculates a virtuallongitudinally disposed reference path which is not necessarily parallelor contiguous with the guideway centreline.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an example of a vehicle according to the prior art, with twosteerable wheelsets and incorporating steering sensors, actuators and acontroller,

FIG. 2 is a wheelset as found in the vehicle in FIG. 1, showing theforces acting at the wheel-to-guideway running faces;

FIG. 3 is a graph representing a typical relationship between side-forceand slip angle for a wheel of the wheelset in FIG. 2, and showing theforce available for steering the wheels;

FIG. 4 shows a schematic representation of a vehicle in accordance witha first embodiment of the present invention,

FIG. 5 shows a schematic representation of a vehicle as shown in FIG. 4when the vehicle is in a turn;

FIG. 6 is a wheelset of the vehicle as shown in FIGS. 4-5, showing theforces acting at the wheel-to-guideway running faces;

FIG. 7 is a graph similar to FIG. 3, showing the force substantiallyavailable to steer the wheels in accordance with the first embodiment ofthe present invention;

FIG. 8 is an illustration of the forces which act on the wheelset of thevehicle shown in FIG. 6.

FIG. 9 is a wheelset and rails as described in a second embodiment ofthe present invention;

FIG. 10 shows a wheelset which is following a longitudinally disposedreference path other than the guideway centreline or secondary runningface, according to a third embodiment of the present invention.

MODE OF CARRYING OUT THE INVENTION

FIGS. 1 and 2 show a vehicle running on a guideway (or track) of thetype described in prior art. Such a vehicle incorporates two steerablewheelsets 1, attached to a vehicle body 2, and each wheelset 1comprising axle 10 and two wheels 12. Steering actuators 3, are used tocontrol the angle of the wheels with respect to the body. Sensors 4,detect the path error between the vehicle and guideway 5. A controller6, processes the signals from the sensors and provides a control outputto steering actuators 3. Upon detecting a path error, wheelsets 1 aresteered in order to minimise the error.

In such a vehicle, axles 10 are substantially horizontal, as shown inFIG. 2. When a lateral force F is applied to the vehicle body 2, it isreacted by the wheel-to-guideway engagement forces. These reactionforces can be resolved into perpendicular components, A_(N) and B_(N),and parallel components, A_(T), B_(T). When a wheel is steered at anangle to its heading, generating a slip angle, small levels of slip atits contact zone generate a lateral force (A_(T), B_(T)). This lateralforce is related to this slip angle, with a typical relationship of theform shown in the graph of FIG. 3. Such a relationship depends on boththe wheel and guideway materials, along with their surface texture andlubrication. The available side force reaches a maximum at a slip angleδ₁, beyond which no additional side force is available. In the exampleshown in FIG. 2, wheelset 1 is steered so that lateral force F isreacted by a combination of A_(T) and B_(T) where A_(T) is equal to C₁as shown graphically in FIG. 3. To generate a force C₁ wheelset 1 mustbe steered so that wheel 12 generates a slip angle δ₀ to its heading.Only the remaining force C₂ is available to steer wheelset 1. If therequired side force exceeds C₂, steering control is lost, the wheelslides in the direction of force F and is unable to follow a desiredpath. In such an event, the wheelset must rely on other means, such aswheel flanges, to ensure it remains safely on the guideway.

FIGS. 4 to 6 show a first embodiment of a vehicle according to thepresent invention comprising steerable wheelsets 21, each comprisingaxle 26 and two wheels 15 running on primary running faces 54 ofguideway 19, attached to vehicle body 16. Steering actuators 17, areused to control the angle of wheelsets 21 with respect to vehicle body16. Sensors 18, detect the lateral displacement between the vehicle andguideway 19. Controller 20 processes the signals from sensors 18, andprovides an output to the steering actuators as a function of thelateral displacement of wheelset 21 with respect to guideway centreline39. Upon detecting a lateral displacement error, wheelsets 21 aresteered in order to minimise the error.

As shown in FIG. 6, axes of rotation 28 of wheels 15 (mounted to stubaxles 25) are inclined downwardly towards guideway centreline 39, as areprimary running faces 54 at the wheel-to-guideway rolling interface.When a lateral force F is similarly applied to vehicle body 16, it isreacted by the wheel-to-guideway engagement forces. These can beresolved into first perpendicular components, P_(N) and Q_(N) and secondparallel components, P_(T) and Q_(T). Each of these has a componentparallel to the applied lateral force F, and in combination reactagainst this force.

On entering a turn, sensors 18 detect the deviation of the vehicle fromguideway centreline 39, and controller 20 responds by steering wheelset21 in the direction to reduce the deviation to zero. The resulting slipangle δ produces lateral forces at the wheel-to-guideway interface,causing the vehicle to accelerate toward the instantaneous centre ofcurvature. The centrifugal force F, acting on the centre of gravity 50of the vehicle, is substantially reacted by an increase in the normalforce, P_(N), on the outer wheel, rather than an increase of thetangential forces, P_(T) and Q_(T). If P_(T) and Q_(T) are small, thenthe wheels do not need to be operating at a very large slip angle δ_(o)as shown in FIG. 7. As a result, most of the maximum availabletangential force, C₂, can be used to steer wheelset 21 and maintain itsalignment with guideway centreline 39.

It is preferred that vehicle centre of gravity 50 and wheels 15 arearranged such that centre of gravity 50 is near the intersection line 52of wheel planes 51. In this configuration, the centrifugal forces orexternal disturbance forces acting on centre of gravity 50, aresubstantially resisted by an increase in the normal force, P_(N), on theouter wheel, and corresponding decrease in the normal force Q_(N) on theinner wheel. As shown in FIG. 8., the difference between the horizontalcomponent P_(H) of P_(N) and the horizontal component Q_(H) Of Q_(N),substantially resists the sum of the centrifugal or external disturbanceforce F.

FIG. 9 depicts a second embodiment of the present invention, where thevehicle has a wheelset 21 comprising wheels 15 adapted to run on aguideway in the form of rails 19. Sensors 18 detect the proximity d₁, d₂of the respective wheel 15 to the respective secondary running face 38on rail 19. Sensed proximities d₁, d₂ are averaged to generate thelateral position of the centreline 49 of the wheelset 21, with respectto the guideway centreline 39. In this embodiment each of the wheelshave a respective flange 37. Flange 37 engages with respective secondaryrunning face 38 on rail 19 in the event of a steering failure, orexcessive side load imparted on the vehicle via lateral acceleration orside wind loads. In other not shown embodiments, sensors 18 may detectthe proximity of the wheels to some other feature on rail 19.

In a third embodiment of the invention as shown in FIG. 10, sensors 18may sense a different path to that of guideway running faces 40. In thisembodiment a longitudinally disposed reference path 41, corresponding tothe guideway centreline 39, is used. However, it should be understoodthat such a path may physically lie between guideway running faces 40,as depicted by phantom lines as reference path 41 a and sensor 18 a, oroutside guideway running faces 40, as depicted by phantom lines asreference path 41 b and sensor 18 b. Alternatively the reference pathmay be a virtual path, bearing some predetermined varying relationshipto the guideway running faces 40.

In other not shown embodiments other means of supporting and steeringthe wheels may be used. These include steering of individual wheelsabout individual steering axes, rather than steering complete wheelset21. Sensors 18, are attached to wheelset 21, and sense its lateraldisplacement with respect to each primary running face 54 of guideway 19and hence with respect to guideway centreline 39. Sensors 18 arepreferably located ahead of wheelset 21 and are connected to controller20. In other not shown embodiments, sensors 18 may be located ahead,beside, and/or even behind the wheels.

Sensors 18, controller 20 and actuators 17 may include hydraulic orelectrical devices and combinations thereof.

It will be recognised by persons skilled in the art that numerousvariations and modifications may be made to the invention withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A vehicle with at least one steerable wheelsetadapted to run on a guideway having two primary running faces laterallyoffset about the centerline of the guideway, and at least one secondaryrunning face lying adjacent to at least one of said primary runningfaces, the wheelset comprising a pair of wheels, each wheel located onopposite sides of the wheelset adapted to engage with a respective oneof the two primary running faces, the vehicle further comprising sensingmeans for sensing lateral displacement of the wheelset with respect tothe at least one secondary running face, the sensing means producing asignal for a control system operably connected to an actuating means tosteer the wheels in response to the sensed lateral displacement, theaxes of rotation of the wheels and the primary running faces areinclined downwardly toward the guideway centerline, and one of thewheels is adapted to engage with the at least one secondary runningface.
 2. A vehicle as claimed in claim 1, wherein each wheel exerts anengagement force with Its respective primary running face, theengagement force on each wheel comprising a perpendicular component toits respective primary running face and a parallel component to itsrespective primary running face substantially perpendicular to theguideway centerline, wherein horizontal forces acting on the wheelsetsubstantially tranversed to the guideway centerline are substantiallyresisted by the sum of the horizontal vectors of the perpendicularcomponents.
 3. A vehicle as claimed in claim 1, wherein each wheelexerts an engagement force with its respective primary running face at acontact zone, the engagement force on each wheel comprising a firstcomponent perpendicular to its respective primary running face and asecond component parallel to its respective primary running facesubstantially transverse to the guideway centerline; wherein a firstplane perpendicular to the axis of rotation of one of the wheels passesthrough the centrcid of its respective contact zone, and a second planeperpendicular to the axis of rotation of the other wheel passes throughthe centroid of its respective contact zone, the first and second planesintersecting along an intersection line disposed above and between thewheels, wherein horizontal forces acting on the wheelset substantiallytransverse to the guideway centerline at or near the intersection lineare substantially resisted by perpendicular components of the engagementforces acting at the primary running faces, such that substantially allof the parallel components of the engagement forces acting at theprimary running faces are available to steer the wheelset.
 4. A vehicleas claimed in claim 3, wherein the intersection line passes through thecenter of gravity of vehicle.
 5. A vehicle as claimed in claim 1,wherein the sensing means comprises at least one sensor located eitherahead or behind the wheelset, or laterally offset with the wheelset.